The present invention concerns a procedure for purifying liquid of solid and dissolved impurities by floatation clarifying/flocculating in which the dirt particles present in a liquid to be purified, along with other separable impurities or impurities dissolved in the liquid and which have been converted into particle form with the aid of a flocculating chemical, are separated from the liquid to be purified and carried to the surface of the liquid to become or form a sludge bed. This sludge bed is conducted to a sludge removal line and then further to a sewer or the equivalent. Flocculating chemicals are added to the liquid thus-purified, through a chemical feeding pipe, whereby the chemicals become mixed with the liquid that requires additional purification and form new particles with the impurities still present in dissolved state in the liquid but which have not yet been removed, in a lower part of a basin. Then, the flocculated liquid is conducted out through a discharge aperture and to further separation. The present invention is also directed to a device for purifying liquid of solid and dissolved impurities by floatation clarifying/flocculating. The floatation method has been used to separate solid particles from liquid for over a hundred years.
With the aid of this method, particles can be caused to rise up and float upon a surface of the liquid, from which the particles can easily be removed and the purified liquid or water then conducted off from underneath.
The surface of the earth comprises a great deal of marshland which could ultimately become the source of usable or drinking water for the population at large. For example, Finland is one of the countries with the largest amount of marshland in the world. The surface waters, lake waters, as well as river waters, in general contain great quantities of organic substances, such as so-called humus generated by flora. Additionally, such water often contains solid substances, such as clay and mud, which make the water muddy. These impurities and contaminants have to be removed from such water, in order to make the same drinkable or usable.
In official regulations promulgated by authorities, rates have been specifically prescribed on what the raw water content should be to be used, so that the water could be used as a raw water source for drinking and household water. However, it is to be noted that such rates have generally been promulgated only recently. Therefore, town and village centers which have already been constructed before such prescriptions on drinking water quality do not frequently have the necessary resources to utilize such water as required in these rates or regulations for providing household water, because such water would not then be available economically.
Additionally, accurate standards have been set forth for the household water to be purified and distributed, such standards having been tightened as the purification methods for water or liquid have become more developed. Water concerning various purification results must meet such standards, before such water is suitable for use. On the other hand, these standards impose additional requirements for the purification processes, so that such purification standards must be reached when using the raw water available.
The flakes or flocs to be produced in the purification process, due to the impurities and with the aid of various chemicals added into the raw water, such flocs containing humus and particles of impurities and requiring removal in the purification process, become very light because of the quality in the raw water, and thus the deposition of such flakes or flocs is slow. Therefore, the horizontal and vertical clarifying procedures which have previously been used exclusively, e.g. in Finland, have been eliminated from use when new purification installations have been constructed, since such processes require a lot of space and large basins for the operation thereof. A so-called floatation method has replaced such procedures, in which flocs are raised to the surface during the purification process with the aid of minute, less than 80 micron air bubbles contained in a water/air solution which is added into the liquid or water. The dirt is removed from the surface and the purified water is conducted away from the bottom, in contrast to the previously-utilized methods.
With the floatation method, great savings are achieved in volume, and therefore also in construction costs, machinery and piping systems. Furthermore, better purification systems have been obtained. Therefore, the floatation method has superseded earlier methods, and is already presently considered to have a remarkable economic significance. It is also extremely useful in enhancing the efficiency of old installations and in improving the quality of the purified water, even without external additional structures.
Often, the raw material to be purified is poor in quality and contains such substances to be eliminated for which one kind of chemical is not alone adequate to solve the problem by being used only once. Furthermore, it may be necessary to use a number of different chemicals such as chemicals containing iron or aluminum which do not perform best when simultaneously used, but do so at different times because the respective reactions take place best at varying pH rates. Therefore, such water requires at least two successive purifications.
The description presented above also concerns purification of residual waters in which good results ar also achieved using the same floatation methods as in purifying household water, but which are now applied for residual waters. The majority of residual water is of such quality that a great part of the impurities can be removed without having to use any chemicals, even exclusively with the floatation method. By purifying the water treated in such a manner again with the aid of chemicals, extremely good results are achieved, for instance in purifying inhabitation residues, residues of the cellulose and paper industries, the paint industry, the pharmaceutical industry, and the food industry, etc. In particular, it can be noted that the majority of solids can be removed in this manner, specifically oil and fatty substances which otherwise considerably interfere with the subsequent purification processes.
Additionally, a plurality of chemicals are also saved and other purifying processing sectors can be made to operate more efficiently. Therefore, the purifying results also become significantly improved, and in addition, savings are achieved in compacting and transporting the sludge away. Furthermore, savings are attained in costs related to water/air solution, equipment, production, distribution, and pumping, which are required in the floatation process because less sludge is formed.